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Electronic Fundamentals

Electronic Fundamentals: Understanding Capacitors

Build a Digital Capacitance Meter

Background Theory of Capacitors

Capacitors Capacitors are one of the most common passive components in circuits just like the resistor. Capacitors store electrical charge and have different functions depending on the circuit design. The capacitance is a measure of how much charge or energy the capacitor can carry. In its most basic form, a capacitor consists of two conducting plates separated by an insulator (dielectric), which is commonly represented with its circuit design symbol. There are many different types of capacitors, made up of various dielectric material, used for many different purposes.

Capacitance is measured in Farads, which is a fairly large unit, so it is most generally used in microfarads (µF, 10-6) or picofarads (pF, 10-12). Capacitors can be either electrolytic or non-electrolytic. Non-electrolytic capacitors can be connected in a circuit in any direction. Electrolytic capacitors must be installed in the correct orientation on the circuit, as one lead is positive and the other negative. Placing electrolytic capacitors will incorrectly prevent your circuit from performing properly, or can even cause them to pop.

Capacitors have an array of applications. They play a critical role in digital electronics as they protect microchips from noise on the power signal by decoupling. Since they can dump their entire charge quickly, they are often used in flashes and lasers along with tuned circuit devices and capacitive sensing devices. Circuits with capacitors display frequency-dependent behavior, so they can be used with circuits that selectively amplify certain frequencies.

Capacitors can be added in series or parallel like resistors, but they are calculated the opposite of resistors. Components connected in series share one common node, and both nodes are shared when in parallel. Resistors in series are added together to find the total resistance, whereas capacitors connected in parallel are added together to find the total capacitance. Resistors in parallel and capacitors in series share the same formula to find the total value, Xeq = (1/[(1/X1+1/X2+...+1/Xn)], just substitute the resistor or capacitor value into X.

Check out how to decipher different types of capacitors, see our circuit notes on capacitors.

The Capacitor Project: Digital Capacitance Meter

This electronics project lets you measure capacitors in a range of capacitance from 0.000pF to 1000µF. That is, a 16x2 LCD Display will be displaying a scale from 0.000pF to 1000uF, whose main components will be an Arduino Uno and the display. If you lose the datasheet and need a quick measurement, this do it yourself project is perfect to perform a quick check.

Time Required: 10 hours depending on experience
Experience Level: Intermediate

Click here to Purchase Capacitance Meter Kit

Capacitance Meter Kit Includes:

Qty.
Component Name Product No.
1
16x2 Character LCD Display - White on Blue 5V DFR0063
1
Arduino Uno R3 DIP Edition (Revision 3) A000066
1
Arduino Uno Proto Shield (PCB only) A000082
1
9V Battery Snap with 2.1mm Barrel Plug 1X9V-2.1 SNAP
1
Cable USB2.0 A/B 3 Feet Black USB-A Male To USB-B Male 10U2-02203-BK
1
Connector Unshrouded Header 40 Position 2.54mm Straight 7000-1X40SG-R
1
Potentiometer 1/4" Square Cermet 1/2W 10KΩ 3362P-1-103LF/76P103LF
1
ABS Plastic Enclosure for Arduino Board - Fits UNO or MEGA M000015
1
6 Position Female Header - Pass through Style for Arduino RS1-06-G-.561-A11596

Required tools and parts:
  • Soldering iron
  • Solder
  • Wire strippers
  • Cutter
  • Needle nose pliers
  • Multimeter
  • Electrical drill
  • Drill bit of 1/16"
  • #22, wire any color, 1 meter
  • A 9V battery

Step 1 – Schematic Diagram

In this step, you are going to concentrate very well in what you will be constructing. That is, this step of your project is crucial since you will need to understand how to connect each component so that the whole project functions correctly. Therefore, this step becomes the main step or an imperative measure so that your project be completed successfully. A larger version will be at the end of the instructions.

Schematic DiagramDigital Capacitance Meter from 0.0001pF to 1000µF
Click to enlarge

Step 2 – 16x2 LCD Display

In this step, you can cut 2x6 pins and put them into the holes of the16x2 LCD Display in the corresponding pins: 1 to 6 & 11 to 16 so that you can have more space for working between the PCB and the Display when this last one be installed.

16 x 2 LCD DisplayLCD Display

Step 3 – 16x2 LCD Display 2

In this step, you are going to do the main connections to the display that you will connect to your Arduino Uno later. Then, you should identify the connections from 16x2 LCD Display in the pins: 4, 6, 11, 12, 13, and 14 that will be connected respectively to the Arduino Uno in the pins: 11, 9, 5, 4, 3, and 2 without forgetting the connections to +5V, GND, and Pot of 10K.

LCD Display ConnectionsLCD Display Connections

Step 4 – 16x2 LCD Display 3

In this step, you are going to match the connections done previously to your LCD Display with the future connections that you will do in the PCB: observe the photo where you can see the details closer.

Match the ConnectionsMatch the Connections

Step 5 – PCB

Once you know how to do the connections between your 16x2 LCD Display and the PCB, you should separate them so that you can install on the PCB: the Connector Unshrouded Headers by utilizing 2x8 pins in the side of the digital pins while using 2 pins in the other side for connecting to GND and +5V.

PCBPCB

Step 6 – PCB Connections

In this step, you are going to connect the GND's so that you can have all GND's connected and so you can install the pot of 10K directly on the GND track and then you can connect it to +5V track as well while completing the connections to this component soldering the central pin to other close track.

PCB ConnectionsPCB Connections

Step 7 – PCB 3

Now, you can do all of connections: that is, preparing the connections and leaving enough space so that can later install the 16x2 LCD Display.

All PCB ConnectionsAll PCB Connections

Step 8 – Joining the PCB & the Display

It's time to match each connection between the PCB and your LCD display so that can later solder correctly each element installed.

Joining the PCB and DisplayJoining the PCB and Display

Step 9 – Joining the PCB & the Display 2

Check carefully the connections in the back side of your PCB so that you can observe if everything is OK with those connections that you did between the PCB and the LCD Display. Obviously, you are going to check the connections done to GND and +5V on the right track as well.

Check Your ConnectionsCheck Your Connections

Step 10 – Completing the Project

Once completed the project, leave clear which the outputs are. That is, it's imperative to define the outputs for this project: in this case, they are A0 for the negative (-) and A4 for the positive (+).

Completing the ProjectCompleting the Project

Step 11 – Getting Ready For Doing Precision Measures

Before uploading the code, you should eliminate the metallic parts of the PCB's holes of A0 and A4 using a drill bit of 1/16" in order to keep '0' (zero) capacitance when the 1x6 Position Female Header - Pass through Style for Arduino Uno is installed.

Making MeasurementsMaking Measurements

Step 12 – Arduino Enclosure

Before installing the Arduino Uno in its enclosure, cut the plastic posts.

Arduino EnclosureArduino Enclosure

Step 13 – Mounting the Shield on the Arduino Uno

Once installed the Arduino Uno inside the enclosure, you can mount the shield on the Arduino Uno.

Mounting the ShieldMounting the Shield

Step 14 – Inserting the 1x6 Position Female Header - Pass through Style for Arduino

In this step, you can insert the 1x6 Position Female Header - Pass through Style for Arduino Uno and so when you upload the code then the cursor will display 0.000pF.

Step 15 – Uploading the Code

Pluging the USB-A to USB-B cable between your project and the computer, upload the code at: http://pastebin.com/njjKZrfv

Next, observe the cursor where you will see 0.000pF.

Uploading the CodeUploading the Code

Step 16 – Using Capacitance Meter

Once uploaded the code from http://pastebin.com/njjKZrfv , unplug the USB-A to USB-B cable that is plugged between the computer and your project so that you can plug your 9V Battery Snap with 2.1mm Barrel Plug and so can also use your 9V battery to get the measure of each capacitor what you want to measure. In this case, I am measuring a 1 pF capacitor. Note that before measuring the capacitor, you can observe in the cursor: 0.000 pF.

Step 17 – Measuring a Capacitor of 10nF


Measurement 10nFMeasurement 10nF

Step 18 – Measuring a Capacitor of 10pF


Measurement 10pFMeasurement 10pF

Step 19 – Measuring a Capacitor of 3.3pF


Measurement 3.3pFMeasurement 3.3pF

Discussion Questions:

What are some applications that use high capacitance?
How do capacitors act differently from AC and DC current?
What kinds of effects can happen to your circuit if your capacitor pops?
How important is discharging the capacitor?